A reverberation device is an electro-acoustic or electronic arrangement for the generation of artificial reverberation .
Electromechanical hall devices
Spring reverb ("reverb spiral")
One or more metallic coil springs are loosely clamped in a frame. The type of clamping enables longitudinal, transverse and torsional vibrations of the spring. Electromechanical converters are attached near the suspensions ( magnet and current-carrying coil ). The magnets are connected to the spring, the coils are firmly attached to the frame.
A current is impressed on the transmitter coil via an amplifier. The amplifier is controlled by the electrical signal to which artificial reverberation is to be applied.
On one side of the suspension, the magnet is made to vibrate by the current in the transmitter coil. The oscillation is propagated on the spring and arrives at the other end of the spring with a slight delay. There the second transducer coil (receiver coil) picks up the oscillation and converts it back into an electrical signal that is decoupled via a second amplifier.
The oscillation is also reflected and travels back and forth on the spring for some time after the input oscillation has subsided. A reverberation effect is created.
In practice, delays of a few 10 ms and reverberation times of a few seconds can be achieved. In practice, however, there are only a few overlapping and thus metallic-sounding individual reflections, since the signal is reflected several times at the spring ends and the spring accordingly passes through several times. In order to produce more echo-like sounds, a significant increase in the frequency of reflection is necessary, so that more diffusivity is created. For this purpose, the spring is deliberately inflicted mechanical damage in the form of etched spots and indented coils. These cause significant disturbances in wave propagation. The desired additional reflections are created.
In addition to the advantage of the simple and thus inexpensive structure, the electro-mechanical spring system has several different undesirable properties:
- The transmission behavior is more or less resonant depending on the design . The sound becomes discolored. By combining several springs with different properties, the transmission behavior (the sound) can be influenced. The input and output amplifier can filter out disruptive resonances to a limited extent through a specific design.
- The delay on the spring is constant, which makes the reverb sound more or less unnatural. Two or three springs are therefore hung in parallel with different delays.
- Better systems with longer delay times can achieve spring lengths of over a meter. In order to save space, the spring is also clamped folded in practice (e.g. in the form of a "Z").
- The spring system can not follow signal impulses due to its inertia , so that a characteristic rattling noise is created.
- Reverberation spirals are sensitive to vibration, airborne noise and structure- borne noise . In order to minimize unwanted background noise, the springs are suspended in an auxiliary frame, which in turn is suspended swinging in a main frame ( decoupling ). The entire system is often built into a soundproof housing.
- There are no parameters that can be varied. Only the addition of the reverb component to the original signal can be set in a mixer ("Reverb" control on many guitar amplifiers).
- The electromagnetic transducers are susceptible to interference from electrical and magnetic fields, which are noticeable as background noise. Bumps against the device also produce a reverb.
A reverb plate works on a similar principle as a spring reverb, but a steel plate is used as the vibrating mechanical system. In contrast to the spring reverb, several parameters can be influenced. With the reverb plate, an almost natural-sounding reverberation can be generated, but due to the required dimensions and the high price, this technology was largely reserved for professional studios.
Tape reverb device
A tape reverb device works with an endless magnetic tape. The audio information is written to or read from the tape using read and write heads. The delay time and the reverb intensity can be set via the speed of the magnetic tape and the volume settings.
Today artificial reverberation is mostly generated electronically in digital signal processors ( DSP ). This method does not have any of the disadvantages of mechanical systems, but a lot of computing power is required if the Hall effect is to be realistically simulated, since a very high number of reflections must be calculated. Simple systems work with feedback memories that lead a signal in attenuated form from their outputs back into the input via several paths. The more memories and paths that are implemented, the more complex the reverb. The aim of developing such devices is as simple an algorithm as possible that can produce the most interesting reverb possible with few resources. Reflection options are also used that cannot actually occur, e.g. B. a reverb that builds up over time. A very computationally time consuming but effective method is the application of a previously obtained reflection pattern to a reflection-free signal in order to simulate real rooms with the help of the FFT .
Mechanical reverb devices are technically out of date. Until the 1970s, they were regularly used in the recording studio next to reverberation rooms to generate reverberation.
Today, however, spring reverb systems (reverb spirals) are still often used in guitar amplifiers for electric guitars , in modular synthesizers and in the Hammond organ . The characteristic sound is reminiscent of the pop music of the 1960s. It is still used in surf music today, especially when it is heavily overdosed . The actually undesirable clattering and splashing at dynamic peaks is consciously used for the sound coloring.
Since the 1980s, artificial reverberation has usually been created using electronic arrangements. The implementation is so inexpensive that even simple mixing consoles for amateur musicians are often equipped with it and are used in their instrument rigs.
- Hall springs were originally used by telephone companies for echo cancellation . Here, the property of delay was used, the reverberation was undesirable.
- In the 1960s, spring reverb devices were available as accessories for hi-fi systems. Among other things, a Hall control was usually attached to tube stereo equipment from Grundig . The reverb device itself was connected externally and was based on Hammond's “reverb spiral”.
- In vehicles of the American brand Imperial , car radios were installed, the rear loudspeaker of which was controlled by a spring reverb  . To disturb z. B. to avoid vibrations while driving, probably a considerable design effort had to be made.
- In the 1960s to 1970s, it was common practice for some rock bands to (not only) destroy their amplifiers at the end of the concert (example: The Who ). The resulting noises were mainly caused by the clattering reverb springs.
- A reverberation spring is mounted in a children's toy currently sold (2005) in the form of a hand microphone , which is stimulated to mechanical vibrations by sound and creates an artificial reverberation when it decays .
- Hall springs can be manipulated mechanically from the outside (e.g. with the hands). The resulting background noise is z. B. used dramaturgically in radio plays and in electronic music .
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
- Roland Enders: The home recording manual. 3rd edition, Carstensen Verlag, Munich, 2003, ISBN 3-910098-25-8
- Gustav Büscher, Alfred Wiegelmann: Little ABC of electroacoustics (= Radio-Praktiker-Bücherei. Vol. 29 / 30a). 6th, completely revised and expanded edition. Franzis, Munich 1972, ISBN 3-7723-0296-3 .
- Hubert Henle: The recording studio manual. Practical introduction to professional recording technology. 5th, completely revised edition. Carstensen, Munich 2001, ISBN 3-910098-19-3 .
- Fritz Kühne: Music transmission systems, planning, construction and maintenance. 5th edition, Franzis Verlag, Munich, 1968
- ↑ Lexicon MPX1. In: archive org. Sound on Sound, June 6, 2015, accessed July 19, 2020 .